One type of semiconductor die, referred to as a "bumped" die includes patterns of contact bumps formed on a face of the die. The contact bumps can be formed on wettable metal contacts on the die in electrical communication with the integrated circuits contained on the die. The contact bumps allow the die to be "flip chip" mounted to a substrate having corresponding solder wettable contacts. This mounting process was originally developed by IBM and is also known as the C4 joining process (Controlled Collapse Chip Connection).
Lead tin alloys (e.g., 95/5 lead tin alloy) and a ball limiting metallurgy (BLM) process can be used to form the bumps. Typically, the bumps are dome shaped, and have an average diameter of from 5 mils to 30 mils. Micro ball grid arrays (BGA) are formed in the smaller range, while standard ball grid arrays are formed in the larger size range. The sides of the bumps typically bow or curve outwardly from flat top surfaces. The flat top surfaces of the bumps form the actual regions of contact with the mating contacts on the substrate.
Contact bumps are also sometimes included in chip scale packages. In general, a "chip scale package" or "chip size package" refers to a package that includes a bare die along with one or more packaging elements. For example, chip scale packages can include thin protective members attached to the face, sides or backside of the die. In addition, chip scale packages can include contact bumps similar to the bumps on bumped dice. Some persons skilled in the art consider a bumped die the simplest form of a chip scale package.
With bumped dice and chip scale packages, it is sometimes necessary to make non-bonded, or temporary, electrical connections with the contact bumps. For example, in the production of Known Good Die (KGD), semiconductor manufacturers are required to test bumped dice prior to shipment. Temporary packages can be used to house a single bare die, or a chip scale package, for burn-in and other test procedure. These types of temporary packages are disclosed in U.S. Pat. Nos. 5,519,332; 5,541,525; 5,495,179; 5,440,240; and 5,408,190 to Wood et al.
Interconnects associated with the temporary packages can be used to electrically contact the bumps on the dice, or on the chip scale packages. With one type of interconnect, indentations on the interconnect can be sized to retain and electrically contact the bumps. For example, this type of interconnect can include a multi layered tape, similar to TAB tape manufactured by Nitto Denko and others. The tape can include a polyimide layer formed with patterns of indentations, and a metal layer subjacent to the indentations. The bumps fit into the indentations and electrically contact the metal layer.
To assist in making this temporary electrical connection, a temporary package can also include a force applying mechanism, such as a spring, adapted to bias the semiconductor component against the interconnect. A contact force must be generated by the force applying mechanism that is sufficient to break through the native oxide covering the bumps. If a sufficient contact force is not generated, then the resultant electrical connection can be poor. However, it is also advantageous to maintain this contact force as low as possible to avoid excessive deformation of the bumps. In particular, the loaded bumps exhibit creep during the burn-in cycles, which are typically performed at elevated temperatures for several hours or more.
In the past, following testing of dice with contact bumps, it has been necessary to reflow the bumps, which are typically damaged by the test procedure. This is an additional process step which adds to the expense and complexity of the testing process. Furthermore, it requires heating the tested dice which can adversely affect the integrated circuitry formed thereon.
Another consideration in testing bumped dice and chip scale packages is the dimensional variations between the contact bumps. The interconnect must be able to accommodate dimensional variations between bumps on different dice or packages, and dimensional variations between individual bumps on the same die or package. These dimensional variations can include the diameter, height, shape, and location of the bumps. In particular, the diameter and z-dimension location (planarity) of the bumps can make the electrical connections difficult to make without high contact forces.
Trapped gases can also cause problems during a reflow procedure. For example, gases can be trapped in cavities formed within the bumps. These trapped gas can expand during a reflow connection process causing the solder material to splatter.
In view of the foregoing, improved interconnects for making electrical connections to semiconductor dice and packages having contact bumps are needed. The present invention is directed to an improved interconnect able to provide a reliable electrical connection with the smallest contact bumps, while minimizing the deformation of the average and large sized contact bumps.